There has been generally known a conventional printer in which a mask is put on the top of a substrate. A solder pool staying on the surface of the mask is pressed and moved on the surface of the mask by a squeegee, whereby solder is applied (printed) onto a predetermined position on the substrate through an opening part formed on the mask. In this printer, the solder pool is formed by accumulating solder that is substantially greater in amount than solder used on a single substrate. When printing using this solder pool, the solder is consumed by repeated printing, and consequently the solder residue in the solder pool decreases gradually. There has been proposed a technology for using a sensor to detect the solder residue in the solder pool and automatically replenishing the solder pool with solder based on the detection result (see Patent Document 1, for example).    Patent Document 1: Japanese Patent Application Publication H6-23945 (Paragraph 0018, FIG. 1)